Dynamo (Generator) Lights: Fact vs Fiction

old fashioned bottle dynamo and rear light with normal bulb

Dynamos (aka generators) are really looked down on by almost all
Americans, and many Brits as well. To the uninitiated, a dynamo sounds
unappealing because it slows you down, makes alot of noise, slips in
the wet, wears out your tires, and the lights aren't very bright and
they go out as soon as you stop moving. In fact, almost all these
things are true of older dynamo systems (where you have a dynamo that
rubs against the side of your tire and powers incandescent lights both
front and rear).

The one thing that is not true, even of older systems, is that the
lights are dim. In fact, even a cheap dynamo front light is brighter
than any small handlebar-mounted battery-powered front light. Just
about the brightest of thse battery-powered lights is the Cateye
HL-MC200 Micro-halogen, which is supposedly a 2.4W light. Dynamo
headlights are also 2.4W when the dynamo is also used to power a .6W
rear light. However dynamo lights are a bit more visible and are a bit
better at lighting up the road than even this light. I think this is
party because the optics used in dynamo lights concentrates the light
where you need it (on a patch of ground right in front of you, and off
to the sides for better side visibility, with very little going
up). It is also partly because alkaline batteries really aren't that
good at supplying the currents demanded of them by bright lights,
while dynamos are very good at providing higher, steady currents. And
you don't need to use the dynamo to power a rear light as well: if you
use a standard battery-powered rear light your light will be 3W which
is quite noticeably brighter than the Cateye Micro-halogen.

When you consider newer systems, you'll find that almost
everything you learned about dynamo lighting systems is wrong. First,
that they slow you down. Well, cheap dynamos that rub your tires still
do slow you down a fair bit, but there are some tire-mounted dynamos
(more properly called bottle dynamos because they are bottle-shaped)
that are very efficient, and so have only minimal drag when powering
your lights. Examples of these are the
Lightspin and
Busch & Mueller
S6 dynamos. These can still slip in the wet and cause some wear to
your tires, but hub dynamos don't.

Hub dynamos take the place of your front hub, and as they spin
they silently generate electricity. They do this very efficiently
indeed, so although they do slow you down a tiny bit, at least
theoretically, you can't even feel the drag. There are two major ones,
made by Shimano
and Schmidt. The
major difference between them is the amount of drag and the cost. The
Schmidt and the Shimano both generate about the same amount of drag
when the lights are on, but the Schmidt has almost no drag when the
lights are off, while the Shimano still has significant drag when
off. The old Shimano hub dynamos used to have the same drag on or off,
but evidently the newer ones have less drag when off. The Schmidt is
obviously better but it costs more than twice the price! The
downsides of hub dynamos are obvious: they weigh a bit more than
bottle dynamos and require you to rebuild your front wheel. You also
need to get a switch to turn on and off your lgihts. These can be a
separate item (Shimano sells a switch that can be used with its hub
dynamo) or can be built into the front lamp (Busch & Mueller make
these, and they work with either Schmidt or Shimano hub dynamos).

B&M dynamo lights with standlights

Seculite Plus

Lumotec Oval Plus

The next misconception is that your lights go off when you stop
going forward. Nowadays you can get dynamo-powered lights with
"standlights". These are LEDs that are powered by a capacitor which
charges up as you ride along, and they stay lit for about 5 mins after
you stop. For rear lights with standlights, usually the light is
itself an LED, so you get the full brightness of the light when you
stop. For front lights, which use halogen bulbs, the standlight is a
separate LED, yellow or white, that comes on when you stop. Thus for
front lights the standlight is quite a bit dimmer than the light you
get while you're moving, but it's still bright enough to help you get
noticed while you are stopped. These lights with standlights are made
by Busch & Mueller
(B&M).

The ideal dynamo-powered setup is a Schmidt hub dynamo powering a
B&M lamp setup such as the Lumotec Oval Senso Plus front light and a
rear light with standlight such as Seculite Plus, 4DLite Plus, or
DToplight Plus. If you don't have as much money you'd save a fair bit
by getting a Shimano hub dynamo, but you should still pay the extra to
get front and rear lights with standlights.

battery-powered DToplight on my commuter bike

One alternative to using the dynamo to power both front and rear
lights, is to use the full power of the dynamo to power your front
light, and to have a separate battery-powered rear light. Ideally the
rear light should be a British standard or European standard LED light
for good brightness both straight behind and from the sides, and for
good battery run-time. This has two main benefits: it allows you to
have a slightly brighter front light, and it makes installing the
system somewhat easier (you don't have to wire up the rear light). The
main disadvantage is that when you turn on your lights you must turn
on both front and rear light separately. This may seem like a minor
issue, but for a commuting bike when you're often riding home at dusk,
it's a good idea to have lights that turn on a quickly and easily as
possible. The ideal setup for this is to have a hub dynamo and an
automatic sensor that turns on the lights when it's dark enough. This
automatic sensor comes with the Shimano hub dynamo switch and with the
Lumotec Oval Senso Plus front light. In both these cases, the front
and rear lights will come on automatically when it gets a bit dark.
My husband has this setup and just leaves the switch setting on
automatic (you can also put it on ON or OFF settings as well), and I
am jealous of his automatic setup.